Tank cleaning machines of the type having rotating spray nozzles have been used for some time. One type, driven by the pressurized cleaning liquid passing through it, is shown in U.S. Pat. No. 3,637,138 to Rucker, the inventor of the present invention. This tank cleaning machine, sold under the trademark GAMAJET II, provides a generally spherical, omni-directional spray pattern. This spray pattern is produced by the movement of the spray nozzles about two perpendicular axes. The tips of the nozzles trace a spherical pattern reminiscent of a ball of twine. Because of the omni-directional nature of the spray pattern, it is quite useful for cleaning the entire interior surface of tanks or other containers.
Some situations, however, do not require or permit liquid cleaner to be sprayed in all directions. For example, open topped fermentation tanks are not good candidates for omni-directional tank cleaning machines. Sometimes, even if a container is covered, it may be desired to apply the liquid cleaner only below a certain point in the container. For example, in certain brewing processes once the tank is empty it should be thoroughly cleaned only below the upper liquid level. This is done to ensure that certain beneficial microbiological organisms are not removed or killed. Thus in these situations omni-directional spray patterns are also not acceptable. In other situations the tank or other container may only have been partially filled and need cleaning only below a certain level. Using an omni-directional tank cleaner would be quite inefficient in these circumstances. In addition, tanks often have a stubborn band of material at some intermediate position along the tank wall, typically at the upper liquid level. In these cases, omni-directional tank cleaning machines would need to be used much longer before the stubborn band is removed compared with the time it would take to clean the remainder of the tank.